1. Field of the Invention
The present invention relates to a portable linear actuator, a method of controlling an electric motor of such an actuator to limit the maximum force generated thereby, and to the use thereof in a machine-part puller or in a tool for working on tubes. The invention also relates to a portable electromechanical tool for working on tubes and including such an actuator.
2. Description of the Related Art
Actuators are known that are capable of exerting forces on the basis of a direct current (DC) electric motor.
Such actuators are connected to specialized tools.
One example of such tools is a machine-part puller for pulling ball bearings. Another example concerns tools for working on tubes for expanding them.
Nevertheless, such actuators are often limited in the maximum force they are capable of producing.
Such actuators are confronted with two types of working situations.
In the first type of situation, the tool is in normal operation. The material against which the tool is applied thus presents resistance that means that the force to be provided by the motor is progressive up to a certain maximum working value which corresponds to the maximum working force on a loaded stroke of the actuator.
In the second type of situation, the tool is put into operation while unloaded. “Operating unloaded” is used to designate a situation in which a tool is connected to the actuator but the tool is not applied against any material or part. Since there is no material to oppose movement of the tool, the force exerted by the actuator is practically zero until the tool reaches the end of its stroke (e.g. because the tube expansion sectors of the tool are at the end of their stroke). Since the tool is then blocked, it generates an instantaneous force on the actuator that is extremely large.
The Applicant has thus observed that the force produced in the second situation can be more than 50% greater than the maximum working force.
This has the drawback of making it necessary to dimension the actuator mechanically in terms of its maximum unloaded force and not of its maximum working force, which in addition to increasing cost, also increases the weight and size of the actuator, and thus makes it less portable.
In addition, the reliability of the actuator is decreased by deteriorating the motor and the mechanism by the sudden increase in the magnitude of the force.
The object of the invention is to remedy those drawbacks.